Relative air humidity influences the function of the tarsal chemoreceptor cells of the cherry fruit fly (Rhagoletis cerasi)

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Abstract
Electrophysiological recordings from the tarsal D‐sensilla of mature, 5–7‐day‐old female European cherry fruit fly (Rhagoletis cerasi L.) revealed that a large proportion of sensilla showed no sensory activity in response to stimulation with the oviposition deterring pheromone (‘ODP’) or sucrose. In contrast, good recordings were obtained from almost all sensilla in freshly emerged, 1‐day‐old flies. Ageing, nutritional state and contamination were excluded as possible major factors influencing the responsiveness of the D‐sensilla. The study of the variability in responsiveness of the sensilla of 1‐day‐old flies among different tarsomers, among tarsi of the same individual and among individuals, revealed that the major source of variability was among individuals.Individual flies were also affected by the humidity in the holding cages: relative air humidity of less then 75% for 4–6 days was shown to reduce the number of D‐sensilla giving recordings with a good signal‐to‐noise ratio. The D‐sensilla on the most distal tarsomers were affected most by the reduced (30–55% r. h.) air humidity. Flies which had contact with plant leaves showed less reduction in responsiveness at low air humidity (40% r. h.) then flies without leaf contact.